The present invention relates to a blind rivet. More specifically, it relates to a blind rivet and fastening method thereof able to fasten a plurality of members to be fastened having large fastening holes using a blind rivet having a washer.
As is well known, a blind rivet includes a hollow metal rivet body having a sleeve and a rivet head on one end of the sleeve, and a metal mandrel having a stem passing through and extending from a through-hole in the rivet body. A blind rivet has the advantage of enabling a plurality of members to be fastened to be worked and fastened from one side.
The rivet body of the blind rivet has a cylindrical hollow sleeve in which a rivet head has been formed on one end and which extends from the rivet head. The mandrel of the blind rivet has a head on one end whose diameter is larger than the inner diameter of the sleeve, and has a stem passing through the rivet body. The mandrel is arranged so that the head of the mandrel is adjacent to the end of the sleeve opposite that of the rivet head, and the stem of the mandrel is inserted into the through-hole in the rivet body so as to extend from the rivet head and complete the assembly of the blind rivet. The assembled blind rivet is inserted into holes in members to be fastened such as panels with the mandrel head at the forward-facing end, and the rivet head is brought into contact with the portion of the member to be fastened surrounding the hole. When the rivet head is held by a fastening tool in this state, and the stem of the mandrel is gripped and pulled out from the rivet head side, the sleeve end of the rivet body is deformed so as to become enlarged in diameter, the mandrel breaks off in the elongated breakable portion of the stem, and the members to be fastened can be fastened between the rivet head and the enlarged end of the sleeve.
As is well known, in a blind rivet, after the mandrel has been pulled out and the sleeve end of the rivet body has been enlarged, the rivet head is squeezed from the outer circumferential surface by the nosepiece of the fastening tool, and the inner circumferential surface of the rivet head engages the stem of the mandrel and is secured. Because the rivet head is squeezed and pushed out in the axial direction, the blind rivet can fasten the members to be fastened in the axial direction with strong crimping force.
However, because the rivet head is to be squeezed, the outer diameter of the rivet head cannot be increased. In a blind rivet, the outer diameter of the rivet head is supposed to be greater than the inner diameter of the holes in the members to be fastened. If the outer diameter of the rivet head were smaller than the inner diameter of the holes in the members to be fastened, the panels could not be fastened.
In a case in which a member to be fastened such as an automobile body panel is fastened to another member to be fastened using a blind rivet, the positions of a plurality of fastening holes in one of the members to be fastened are aligned with the positions of a plurality of fastening holes in the other member to be fastened, and the members to be fastened are fastened with a blind rivet in each fastening hole. Generally, the inner diameter of the fastening holes in one of the members to be fastened (the blind side) is somewhat larger than the outer diameter of the hollow sleeve of the rivet body. The inner diameter of the fastening holes in the other member to be fastened (working side) is larger than the fastening holes in the member to be fastened on the blind side. These fastening holes (clearance holes) compensate for any position error in the fastening holes of the members to be fastened. Thus, members to be fastened in which the inner diameter of one of the members to be fastened is greater than the inner diameter of the other member to be fastened cannot be fastened together using a blind rivet in which the outer diameter of the rivet head is small.
This problem can be solved using a blind rivet in which a flange having a large outer diameter is integrally formed with the rivet head. Members to be fastened having fastening holes with a large inner diameter can be fastened using one of these blind rivets. However, when two members to be fastened are fastened together using a rivet body having a large-diameter flange, the two members to be fastened cannot be fastened together with sufficient crimping force.
When a blind rivet is fastened by squeezing the rivet head, the rivet head is squeezed by the nosepiece of the fastening tool and the rivet head is pushed out in the axial direction. This action forcibly interposes the two members to be fastened between the rivet head pushed out in the axial direction and the enlarged end of the sleeve, generating crimping force.
However, when a flange is integrally formed with the rivet head, the force pushing out the rivet head in the axial direction is blocked by the flange. As a result, crimping force strong enough to crimp the members to be fastened is not generated, and sufficient fastening force cannot be obtained.